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Heavy metal free, environmentally green percussion primer and ordnance and systems incorporating sameRelated Patent Categories: Explosive And Thermic Compositions Or Charges, Containing Inorganic Nitrogen-oxygen Salt, Ammonium NitrateHeavy metal free, environmentally green percussion primer and ordnance and systems incorporating same description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060219341, Heavy metal free, environmentally green percussion primer and ordnance and systems incorporating same. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to a percussion primer that is nontoxic, noncorrosive, and nonhygroscopic. More specifically, the present invention relates to a percussion primer that includes a sensitized explosive, an oxidizer, and a melt binder, as well as to ordnance and systems incorporating such a percussion primer. BACKGROUND OF THE INVENTION [0002] A percussion primer is a primary explosive composition that is commonly used to ignite a secondary explosive composition or charge. The primary explosive composition is more sensitive to impact than the secondary explosive composition and burns or deflagrates for a short period of time before detonating. To be effective as a percussion primer, the primary explosive composition must have a relatively low activation energy for a given output energy. In contrast, conventional explosives and insensitive explosives with similar output energies have higher activation energies. Since the primary explosive composition is more sensitive to impact, the primary explosive composition ignites and detonates before the secondary explosive composition. In contrast, the secondary explosive composition is relatively stable and does not detonate until initiated by the primary explosive composition. [0003] Many ingredients of conventional percussion primers are toxic and their use is restricted by the Environmental Protection Agency. These ingredients include styphnate and picrate salts, heavy metal compounds, or diazodinitrophenol ("DDNP" or dinol). The heavy metal compounds include compounds of mercury, lead, barium, antimony, beryllium, cesium, cadmium, arsenic, chromium, selenium, strontium, tin, or thallium, such as lead styphnate or barium styphnate, or mercury fulminate. Upon ignition, a percussion primer that includes one of these ingredients emits toxic lead oxides or toxic compounds of other heavy metals, such as oxides of cesium, barium, antimony, or strontium. DDNP is also toxic because it is known to cause allergic reactions and is possibly carcinogenic. [0004] Conventional percussion primers also commonly include oxidizers, such as potassium nitrate, potassium perchlorate, or potassium chlorate, which are also toxic. Potassium nitrate and potassium chlorate are also hygroscopic, which increases the complexity of processing the percussion primer because the potassium nitrate and potassium chlorate must be stored in ovens and cannot be used on wet days. In addition to requiring specialized storage, hygroscopic materials cause the percussion primer to have a sticky consistency, which affects loading and processing of the percussion primer. Other hygroscopic ingredients, such as gums, are also used in conventional percussion primers. Gums typically gain about 30% of the gum weight in moisture when exposed to humid conditions. In addition to being hygroscopic, gums are obtained from natural sources and, therefore, exhibit characteristics which may vary from batch to batch. Some ingredients of conventional percussion primers are also corrosive, such as potassium chlorate, which is corrosive to steel and corrodes a gun barrel when the percussion primer is used in small arms ammunition. [0005] To reduce health and environmental risks, percussion primers that are free of lead have been developed. U.S. Pat. No. 4,522,665 to Yates, Jr. et al. discloses a percussion primer that includes titanium and potassium perchlorate. U.S. Pat. No. 5,417,160 to Mei et al. discloses a percussion primer that contains calcium silicide, DDNP, and an alkaline or alkaline earth nitrate. U.S. Pat. No. 5,167,736 to Mei et al. discloses a percussion primer that includes DDNP and boron and U.S. Pat. No. 5,567,252 to Mei et al. discloses a percussion primer that includes DDNP, boron, and iron oxide. U.S. Pat. Nos. 4,963,201 and 5,216,199 to Bjerke et al. disclose a percussion primer that includes DDNP, strontium nitrate, tetracene, and a nitrate ester fuel. U.S. Pat. No. 6,478,903 to John, Jr. et al. discloses a percussion primer that includes bismuth sulfide and potassium nitrate or zinc sulfide and aluminum nitrate. U.S. Pat. No. 4,581,082 to Hagel et al. discloses a primer charge that includes zinc peroxide, DDNP, and/or a strontium salt of mono- and/or dinitrodihydroxydiazobenzene. [0006] International Application WO 01/21558 to Nesveda et al. discloses an ignition mixture that includes a high explosive and a sensibilizer, such as tetracene, tetrazole, a tetrazole derivative, or a tetrazole salt. The high explosive is a nitroester, such as penthrite, nitrocellulose, or hexanitromanite, or a nitramine, such as hexogen ("RDX"), octogen ("HMX"), or tetryl. The ignition mixture also includes powdered boron as a fuel and an oxidizing agent, such as an oxide of copper, bismuth, zinc, iron, manganese, vanadium, tin, molybdenum, or calcium. [0007] In light of the problems mentioned above with conventional percussion primers, it would be desirable to produce a percussion primer that utilizes nontoxic, noncorrosive, and nonhygroscopic ingredients. BRIEF SUMMARY OF THE INVENTION [0008] The present invention relates to a sensitized explosive that comprises an explosive precipitated onto a sensitizer. The explosive is selected from the group consisting of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0.sup.5,90.- sup.3,11]-dodecane ("CL-20"), pentaerythritol tetranitrate ("PETN"), cyclo-1,3,5-trimethylene-2,4,6-trinitramine ("RDX"), cyclotetramethylene tetranitramine ("HMX"), and mixtures thereof. The sensitizer is selected from the group consisting of aluminum, aluminum oxide, titanium, zirconium, magnesium, boron, silicon, melamine, styrene, lithium aluminum hydride, calcium silicide, and mixtures thereof. The explosive may comprise from approximately 70% by weight ("wt %") to approximately 99.5 wt % of a total weight of the sensitized explosive and the sensitizer may comprise from approximately 0.5 wt % to approximately 30 wt % of the total weight of the sensitized explosive. The sensitized explosive may have a particle size that ranges from approximately 1 .mu.m to approximately 100 .mu.m. [0009] The present invention also relates to a percussion primer that comprises a sensitized explosive, a bismuth compound, and a melt binder, wherein the sensitized explosive comprises an explosive precipitated onto a sensitizer. The explosive may have an impact sensitivity that ranges from approximately 0.3 kp m to approximately 0.75 kp m. The explosive and the sensitizer may be one of the compounds previously described and may be present in the amounts indicated above. The bismuth compound may be bismuth oxide, bismuth subnitrate, bismuth tetroxide, bismuth sulfide, or mixtures thereof. The melt binder may be a wax having a melting point above ambient temperature, trinitrotoluene, poly(3,3-bis(azidomethyl)oxetane), poly(3-azidomethyl-3-methyloxetane), ethyl-3,5-dinitrobenzoate, 1,3,3-trinitroazetine, natural gums, or mixtures thereof. [0010] The sensitized explosive may comprise from approximately 35 wt % to approximately 55 wt % of a total weight of the percussion primer, the bismuth compound may comprise from approximately 20 wt % to approximately 75 wt % of the total weight of the percussion primer, and the melt binder may comprise from approximately 0.5 wt % to less than approximately 20 wt % of the total weight of the percussion primer. The percussion primer may further comprise at least one of ground glass, nitrocellulose, and tetracene. [0011] The present invention also relates to a method of producing the sensitized explosive that comprises precipitating an explosive onto a sensitizer. The explosive is selected from the group consisting of CL-20, PETN, RDX, and HMX and the sensitizer is selected from the group consisting of aluminum, aluminum oxide, titanium, zirconium, magnesium, boron, silicon, melamine, styrene, lithium aluminum hydride, calcium silicide, and mixtures thereof. To precipitate the explosive, the explosive may be dissolved in a solvent, the sensitizer added to the solvent, and the solvent removed, forming crystals of the sensitized explosive. The crystals may have a particle size that ranges from approximately 1.0 .mu.m to approximately 100 .mu.m. [0012] The present invention also relates to a method of producing the percussion primer that comprises providing a sensitized explosive and combining the sensitized explosive with a bismuth compound and a melt binder. The sensitized explosive is produced as described above. The bismuth compound and the melt binder are as described above. [0013] The present invention also relates to a gun cartridge that comprises a casing in which a percussion primer and a secondary explosive composition are disposed. The percussion primer is as described above. The gun cartridge may be a centerfire gun cartridge or a rimfire gun cartridge. [0014] The present invention also relates to primer-containing ordnance assemblies comprising a housing in which a percussion primer and a secondary explosive composition are disposed. The percussion primer is as described above. The primer-containing ordnance assembly may be (without limitation) a grenade, mortar, detcord initiator, mortar round, rocket motor, or other system including a percussion primer and secondary explosive composition, alone or in combination with a propellant. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS [0015] While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, the advantages of this invention may be more readily ascertained from the following description of the invention when read in conjunction with the accompanying drawings in which: [0016] FIG. 1 is a scanning electron micrograph of crystals of CL-20 sensitized with aluminum; [0017] FIGS. 2A and 2B are cross-sectional views of a rimfire gun cartridge; [0018] FIGS. 3A and 3B are cross-sectional views of a centerfire gun cartridge; [0019] FIG. 4 is a schematic illustration of exemplary ordnance in which a percussion primer of the present invention is used; and [0020] FIGS. 5 and 6 show the results of Allegheny Ballistics Laboratory ("ABL") impact testing conducted on sensitized explosives. 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